USE/CARE OF HANDTOOLS & MEASURING TOOLS - OD1621 - LESSON 3/TASK 1
FIGURE 151. CONVERSION CHART - FRACTIONS OF AN INCH
TO DECIMALS OF AN INCH, AND MILLIMETERS.
(1) Inch Measure Systems.
(a) Whitworth. Introduced in England in 1841. The thread form is
based on a 55 thread angle, and the crest and roots are rounded.
(b) American National. The American National screw thread system
This system is based on 60 thread angle and flat
was developed in 1933.
crests and roots; it includes the following series:
1 Coarse thread sizes of 1 to 12 and 1/4 to 4 inches.